The invention relates to a waveguide plate and a process for its production and a microtitre plate comprising such a waveguide plate and as used, for example, for analytical purposes in the biochemical and medical sector, as well as a sensor platform based on a waveguide plate, an evanescent field sensor plate, according to the invention as well as arrangements of sample compartments, with a waveguide plate or a sensor platform according to the invention as a boundary surface of said arrangement of sample compartments. The invention also relates to an optical coupler and a device for monitoring such a coupler.
The process according to the invention is suitable for producing optical elements with grating structures. Evanescent field sensor plates and microtitre plates produced according to the process can be used in chemical and biomolecular analyses. Optical couplers have applications in communications technology, and more particularly in data transmission via fibre networks. A potential application of a particular coupler according to the invention is in a device for monitoring the wavelength of laser light in a fiber network.
EP-A-0 602 829 discloses a process for producing a grating structure on a substrate, for example for a DBR semiconductor laser, in which first a phase mask is produced and then the substrate, e.g. InP, is exposed at the Lithrow angle, through the phase mask. The exposure can be effected by means of an Hg-Xe arc lamp having a light source diameter of 0.25 mm, three lines around 365 nm wavelength being filtered out. The substrate is located close to the phase mask, i.e. at a distance of not more than 10 microns.
To produce the phase mask, a quartz substrate is covered with three layers, a photoresist layer, a thin germanium layer and finally a layer of a resist sensitive to electron beams. The uppermost layer is then structured by inscribing by means of electron beams, developing the uppermost layer and removing the unexposed parts. The structure is transferred to the layers underneath by reactive ion etching, initially with CF3Br and then with O2, and finally to the quartz substrate itself by a further step of reactive ion etching, whereupon the residues of the layers are removed. The grating constant may be, for example, between 190 nm and 250 nm. The phase mask may be several centimeters long and the grating may extend over its entire length. However, the length of the lines is, as a rule, only 5–20 microns. Greater lengths are possible but require very long processing times. In practice, gratings of more than 1 mm2 can hardly be produced with reasonable effort and good accuracy. In particular, stitching errors during inscribing by means of electron beams cannot be avoided.
From U.S. Pat. No. 5,675,691 a plate is known on which coupling gratings are produced by applying a layer of TiO2, Ta2O5, HfO2, Y2O3, Al2O3, Nb2O5, nitride or oxynitride of Al, Si or Hf to a substrate of glass, in particular quartz glass, ceramic, or predominantly organic material. It is being possible to provide a 20 nm thick intermediate layer, e.g. of SiO2, and to structure it by ablation or modification of the refractive index by means of exposure to two superimposed beams of an excimer laser or to a beam modified by a mask. Instead, it is also possible to structure an intermediate layer, e.g. of TiO2, in which the ablation barrier is lower and which is applied either to the layer or directly to the substrate and, in the latter case, is superimposed by the layer after structuring. The grating periods are, for example, 375 nm or 440 nm. The grating surface area is freely selectable and may be, for example, 1 mm×1 mm or 8 mm×8 mm.
From U.S. Pat. No. 5,822,472 an evanescent field sensor plate for chemical analyses is known which bears a 40 nm to 160 nm thick layer of TiO2, ZnO, Nb2O5, Ta2O5, HfO2 or ZrO2 on a support of plastic, glass or quartz. An intermediate layer of nonluminescent material with a low refractive index, e.g., quartz having a thickness of 100 nm, for example, which at the same time serves as an adhesion promoter, may be arranged in between. An input coupling grating and an output coupling grating are provided which are created by known photolithographic or holographic and etching methods, either in the support or in the layer, and have a grating period of between 200 nm and 1000 nm. The gratings may have dimensions of 2 mm (parallel to the lines)×4 mm, with a total surface area of the wave-guide plate of 12 mm×20 mm.
From J. Duebendorfer and R. E. Kunz: “Compact integrated optical immunosensor using replicated chirped coupling grating sensor chips”, Applied Optics, 37/10 (1 Apr. 1998), a further evanescent field sensor plate comprising a polycarbonate support plate is known into which a modulated input coupling grating having a grating period varying between 420 nm and 422.8 nm and an output coupling grating having a grating period varying between 595.1 nm and 600.8 nm were embossed. Thereafter, a TiO2 layer having a thickness of 137 nm and a refractive index of 2.346 was applied by means of low-temperature DC magnetron sputtering, and finally the evanescent field sensor plate was silanised. The input coupling angle is about −9.5_ and the output coupling angle is about 22.5_.
From U.S. Pat. No. 5,738,825 a microtitre plate can be obtained which has a 20 nm to 1000 nm, preferably 30 nm to 500 nm thick layer of TiO2, Ta2O5, HfO2, ZrO2, SiO2, Si3N4, Al2O3, Nb2O5 nitride or oxynitride of Al, Si or Hf applied to its bottom surface, this layer being covered by a plastic layer. Input and output coupling gratings are mounted underneath each cavity. The gratings have a grating period between 330 nm and 1000 nm, in particular about 400 nm to 800 nm, and are produced by lithographic or mechanical methods.
From CH-A-688 165 a wave-guide plate comprising a substrate of plastic, e.g. polycarbonate, is known whose surface was structured mechanically—by deep drawing, embossing or during its injection moulding—and in particular provided with a coupling grating, and bears a layer of TiO2, Ta2O5, ZrO2, Al2O3, SiO2—TiO2, HfO2, Y2O3, Nb2O5, silicon nitride, oxynitride, SiOxNy, HfOxNy, AlOxNy, TiOxNy, MgF2 or CaF2 applied by a PVD method. To reduce the attenuation losses, an approximately 20 nm thick intermediate layer applied to the substrate prior to the layer and comprising an inorganic dielectric material such as SiO2 is provided which at the same time serves as an adhesion promoter.
All plates described above are produced by processes with which no satisfactory uniformity of the coupling grating can be achieved, so that the coupling angle varies relatively widely. Consequently, the relative angular position of the exposure unit and plate must be optimised laboriously in each step when the plate is to be used as a waveguide or an evanescent field sensor plate. The filter characteristics are unsatisfactory and not sufficient, for instance, for selectively filtering a particular wavelength from a group of very closely spaced wavelengths, when the plate is used as an optical coupler in communications technology. Some of the processes described are also very laborious or do not allow very large numbers of pieces of constant quality to be made.